Humeral arthroplasty

Abstract

Arthroplasty components include an articular surface and a bone-facing surface. The bone-facing surface includes a concave arrangement of planar surfaces which converge as they approach a middle portion of the articular surface. Instruments and implantation methods are also disclosed.

The invention claimed is: 
     
       1. An arthroplasty system, comprising:
 a small size prosthesis with an articular surface having a small radius; 
 a medium size prosthesis with an articular surface having a medium radius; and 
 a large size prosthesis with an articular surface having a large radius; 
 wherein the articular surfaces of the small, medium, and large size prostheses and the small, medium, and large radii are all spherical, all ellipsoidal, or all ovoid; 
 wherein the articular surfaces of the small, medium, and large size prostheses pass through a first pair of points on opposite sides of a defined gage circle which has a fixed relationship to a group of bone-facing features common to the small, medium, and large size prostheses; 
 wherein the small, medium, and large size prostheses require the same bone preparation. 
 
     
     
       2. The system of  claim 1 , wherein the group of bone-facing features comprises first, second, and third planar surfaces that intersect at a first point, wherein the first and second planar surfaces intersect at a first line that includes the first point, wherein the first line lies in a common plane with the defined gage circle. 
     
     
       3. The system of  claim 1 , comprising:
 a reamer comprising a distal working portion and a shaft extending proximally from the distal working portion, wherein the distal working portion comprises bone-facing cutting features encircled by a continuous smooth perimeter surface having an inner edge that corresponds to the defined gage circle, so that in use, the bone-facing cutting features cut bone as the reamer is advanced until the inner edge contacts bone to stop further bone removal by the reamer. 
 
     
     
       4. An arthroplasty system, comprising:
 a first prosthesis comprising a first articular surface and a first bone-facing side opposite the first articular surface, wherein the first articular surface comprises a first radius, wherein the first bone-facing side comprises a first concave arrangement of at least three planar surfaces that all intersect at a first point on the first bone-facing side; 
 a second prosthesis comprising a second articular surface and a second bone-facing side opposite the second articular surface, wherein the second articular surface comprises a second radius, wherein the second bone-facing side comprises a second concave arrangement of at least three planar surfaces that all intersect at a second point on the second bone-facing side; and 
 a third prosthesis comprising a third articular surface and a third bone-facing side opposite the third articular surface, wherein the third articular surface comprises a third radius, wherein the third bone-facing side comprises a third concave arrangement of at least three planar surfaces that all intersect at a third point on the third bone-facing side; 
 wherein the first, second, and third articular surfaces and the first, second, and third radii are selected from the group consisting of a set of spherical surfaces and radii, a set of ellipsoidal surfaces and radii, and a set of ovoid surfaces and radii; 
 wherein the second radius is a different size than the first radius; 
 wherein the third radius is a different size than the first and second radii; 
 wherein, when the first, second, and third prostheses are superimposed, the first, second, and third concave arrangements superimpose exactly, and the first, second, and third articular surfaces pass through fourth and fifth points which are on opposite sides of a circle. 
 
     
     
       5. The system of  claim 4 , wherein
 the first concave arrangement comprises first, second, and third planar surfaces, wherein the first, second, and third planar surfaces intersect at the first point; and 
 the second concave arrangement comprises fourth, fifth, and sixth planar surfaces, wherein the fourth, fifth, and sixth planar surfaces intersect at the second point; 
 wherein, when the first and second prostheses are superimposed, the first and fourth planar surfaces are coplanar, the second and fifth planar surfaces are coplanar, the third and sixth planar surfaces are coplanar, and the first and second points are coincident. 
 
     
     
       6. The system of  claim 5 , wherein
 the third concave arrangement comprises seventh, eighth, and ninth planar surfaces, wherein the seventh, eighth, and ninth planar surfaces intersect at the third point; 
 wherein, when the first, second, and third prostheses are superimposed, the first, fourth, and seventh planar surfaces are coplanar, the second, fifth, and eighth planar surfaces are coplanar, the third, sixth, and ninth planar surfaces are coplanar, and the first, second, and third points are coincident. 
 
     
     
       7. An arthroplasty system, comprising:
 a first prosthesis comprising a first articular surface and a first bone-facing side opposite the first articular surface, wherein the first articular surface comprises a first radius, wherein the first bone-facing side comprises a first concave arrangement of at least three planar surfaces that all intersect at a first point on the first bone-facing side; 
 a second prosthesis comprising a second articular surface and a second bone-facing side opposite the second articular surface, wherein the second articular surface comprises a second radius, wherein the second bone-facing side comprises a second concave arrangement of at least three planar surfaces that all intersect at a second point on the second bone-facing side; and 
 a third prosthesis comprising a third articular surface and a third bone-facing side opposite the third articular surface, wherein the third articular surface comprises a third radius, wherein the third bone-facing side comprises a third concave arrangement of at least three planar surfaces that all intersect at a third point on the third bone-facing side; 
 wherein the first, second, and third articular surfaces are ellipsoidal surfaces, wherein the first, second, and third radii are ellipsoidal radii; 
 wherein the second radius is a different size than the first radius; 
 wherein the third radius is a different size than the first and second radii; 
 wherein, when the first, second, and third prostheses are superimposed, the first, second, and third concave arrangements superimpose exactly, and the first, second, and third radii pass through a first pair of points on opposite sides of a first gage circle. 
 
     
     
       8. The system of  claim 7 , wherein
 the first articular surface comprises an ellipsoidal fourth radius lying in a plane transverse to the first radius, wherein the fourth radius is a different size than the first radius; 
 the second articular surface comprises an ellipsoidal fifth radius lying in a plane transverse to the second radius, wherein the fifth radius is a different size than the second radius; and 
 the third articular surface comprises an ellipsoidal sixth radius lying in a plane transverse to the third radius, wherein the sixth radius is a different size than the third radius; 
 wherein the fourth, fifth, and sixth radii are different sizes; 
 wherein, when the first, second, and third prostheses are superimposed, the fourth, fifth, and sixth radii pass through a second pair of points on opposite sides of a second gage circle, wherein the first and second gage circles lie in a common plane. 
 
     
     
       9. The system of  claim 7 , wherein the second radius is larger than the first radius, wherein, when the first and second prostheses are superimposed, the first radius protrudes farther above the first gage circle, away from the first and second bone-facing sides, than does the second radius. 
     
     
       10. An arthroplasty system, comprising:
 a first prosthesis comprising a first articular surface and a first bone-facing side opposite the first articular surface, wherein the first articular surface comprises a first radius, wherein the first bone-facing side comprises first and second planar surfaces that intersect to form a first line; 
 a second prosthesis comprising a second articular surface and a second bone-facing side opposite the second articular surface, wherein the second articular surface comprises a second radius, wherein the second bone-facing side comprises third and fourth planar surfaces that intersect to form a second line, wherein the first and second radii are different sizes, wherein, when the first and second prostheses are superimposed, the first and third planar surfaces are coplanar, the second and fourth planar surfaces are coplanar, the first and second lines are collinear, and the first and second articular surfaces intersect at a gage circle; and 
 a reamer comprising a distal working portion and a shaft extending proximally from the distal working portion, wherein the distal working portion comprises a round perimeter rim encircling a bone-facing cutting feature, wherein the rim comprises a continuous smooth surface having an inner edge that corresponds to the defined gage circle, so that in use, the bone-facing cutting feature cuts a bone as the reamer is advanced toward the bone until the inner edge contacts the bone to stop further bone removal by the reamer. 
 
     
     
       11. The system of  claim 10 , comprising:
 a third prosthesis comprising a third articular surface and a third bone-facing side opposite the third articular surface, wherein the third articular surface comprises a third radius, wherein the third bone-facing side comprises fifth and sixth planar surfaces that intersect to form a third line; 
 wherein the first, second, and third radii are different sizes; 
 wherein, when the first, second, and third prostheses are superimposed, the first, third, and fifth planar surfaces are coplanar, the second, fourth, and sixth planar surfaces are coplanar, the first, second, and third lines are collinear, and the first, second, and third articular surfaces all intersect at the gage circle. 
 
     
     
       12. The system of  claim 10 , wherein the gage circle and the first and second lines lie in a common plane. 
     
     
       13. The system of  claim 10 , wherein the second radius is larger than the first radius, wherein, when the first and second prostheses are superimposed, the first radius protrudes farther above the gage circle, away from the first and second bone-facing sides, than does the second radius. 
     
     
       14. An arthroplasty system, comprising:
 a small size prosthesis with an articular surface having a small radius; 
 a large size prosthesis with an articular surface having a large radius, wherein the articular surfaces of the small and large size prostheses pass through a defined gage circle which has a fixed relationship to a group of bone-facing features common to the small and large size prostheses, wherein the small and large size prostheses require the same bone preparation; and 
 a reamer comprising a distal working portion and a shaft extending proximally from the distal working portion, wherein the distal working portion comprises bone-facing cutting features encircled by a continuous smooth perimeter surface having an inner edge that corresponds to the defined gage circle, so that in use, the bone-facing cutting features cut bone as the reamer is advanced until the inner edge contacts bone to stop further bone removal by the reamer. 
 
     
     
       15. The system of  claim 14 , comprising:
 a medium size prosthesis with an articular surface having a medium radius; 
 wherein the articular surfaces of the small, medium, and large size prostheses pass through the defined gage circle which has a fixed relationship to a group of bone-facing features common to the small, medium, and large size prostheses; 
 wherein the small, medium, and large size prostheses require the same bone preparation. 
 
     
     
       16. The system of  claim 14 , wherein the group of bone-facing features comprises first, second, and third planar surfaces that intersect at a first point, wherein the first and second planar surfaces intersect at a first line that includes the first point, wherein the first line lies in a common plane with the defined gage circle.